[Suggestion] Add distrobox-edit, to allow editable distroboxes

[lp35]

Is your feature request related to a problem? Please describe.

Hey! Firt thank you very much for this awesome project!

Sometime we create a new box, and after a while we need to add an option (e.g --nvidia, or a mountpoint)

Describe the solution you'd like

Thi would be great to be able to use a command like distrobox-edit, allowing to modify exisiting boxes!

Describe alternatives you've considered

None

Thanks!